The decision to replant part or all of a field--for whatever the reason--is not always an easy one. It's often difficult to assess just how badly the stand of corn or soybeans is damaged, and even more difficult to determine if remaining plants in drowned out low areas or one affected by a frost or freeze (like the one that hit much of Iowa this week) will recover and, if they do, how much that damage will affect overall yield.
The following information on making and evaluating replanting decisions is provided by the On-Farm Network, sponsored by the Iowa Soybean Association.
Follow these guidelines for evaluating a problem corn or soybean stand and making replanting decisions
While a number of conditions can cause us to consider replanting, there are many times the decision is not clear, and the data to guide it is limited. Iowa State University Extension has a couple of good web pages that can help in deciding whether to replant. Click here for the first, and here for the second. ISU Ag Economist William Edwards also has a developed a replant calculator, based on price expectations and the extra costs associated with replanting that might be helpful. Click here to download an Excel version you can use on your computer.
It is interesting that many growers who do on-farm replicated strip testing for things like fertilizer rates or hybrids typically don't leave strips to see if their decision to replant was correct. Perhaps, they don't want to know if they were right after agonizing over the decision.
Aerial imagery of stands, as the photos are taken later in the season, are a good learning tool
However, there are tools that can help determine if your decisions were correct. Aerial imagery of the field in question can help provide some feedback on replant decisions. (Since plants are small and there's no crop canopy, it's not possible to use aerial imagery to assess lost stand early in the season, at the time of replant). However, we can show you a few images from later in the season in previous years that show differences that can be helpful in evaluating the decision after the fact, and, hopefully, will be useful in the future.
The image on the left shows multiple areas of replant. There is a large replanted area at the top of the image. Notice in the transition between the original planting and the replanted area there is a lot of soil showing where the stand is very thin. In hindsight, the replant probably should have gone further, filling in the transition area as much as possible. In the middle part of the field, you see an area of the field that appears to have been the result of four different plantings, leaving sort of a bulls-eye made by the "rings" of replant.
Click here to access aerial imagery from your farm from previous years to see what you can learn about areas with frequent replant or stand problems. Tile drainage has helped many growers avoid plant stand losses to wet soil, and for some, it's done away with the perennial decision of where and how much replanting is needed. There are several presentations from past On-Farm Network conferences than can provide more information about remote sensing. To access these, click here for the On-Farm Network home page, then mouse over "On-Farm Network Conference" for a drop down menu that will allow you to access presentations from the 2011 and 2010 conferences.